Necrogammarus

Necrogammarus; Temporal range: Late Silurian, 422.9–418.7 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Illustration of In.43786, the holotype (and only known) specimen of N. salweyi.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	† Eurypterida
Superfamily:	† Pterygotioidea
Family:	† Pterygotidae
Genus:	† Necrogammarus ; Woodward, 1870
Species:	†N. salweyi
Binomial name
	†Necrogammarus salweyi; Woodward, 1870

Last updated October 05, 2024

Necrogammarus salweyi is the binomial name applied to an arthropod fossil discovered in Herefordshire, England. The fossil represents a fragmentary section of the underside and an appendage of a pterygotid eurypterid, a group of large and predatory aquatic arthropods that lived from the late Silurian to the late Devonian. The Necrogammarus fossil is Late Silurian in age and its generic name means "dead lobster", deriving from Ancient Greek νεκρός (nekrós, “dead body”) and Latin gammarus ("lobster").

Historically classified as either a millipede or a crustacean (hence the name) and once considered to potentially represent the oldest myriapod in the fossil record, Necrogammarus was first revealed to represent a fragmentary section of a large pterygotid eurypterid in 1986 by the researcher Paul Selden. As two large pterygotids are already known from the same locality and same timespan as Necrogammarus, Erettopterus and Pterygotus , it is possible that the Necrogammarus remains, in reality, belong to one of these genera. As both genera are only diagnosed and differentiated from each other by features in body parts absent in the Necrogammarus fossil, such as the chelicerae (frontal appendages) and coxae (leg segments), it is impossible to assign Necrogammarus to either of them for the time being.

Pterygotids are differentiated from other eurypterids by their flattened telsons (the most posterior segment of the body) and their modified chelicerae (frontal appendages), ending in well-developed chelae (claws). Regardless of its potential identity as either Pterygotus or Erettopterus, these features are likely to have been present in Necrogammarus as well, as all other members of the family possess them.

History of research

The Necrogammarus fossil was collected by Humphrey Salwey at Church Hill quarry in Leintwardine, a village in Herefordshire, England. The specific deposits from which the fossil were uncovered are part of the Lower Leintwardine Beds or the Middle Elton Beds, both Ludlow (Late Silurian) in age.^[1]

The specimen, designated with the specimen number In.43786 and housed at the British Museum of Natural History,^[2] was first described by the prominent eurypterid researchers John William Salter and Thomas Henry Huxley in 1859. Though the two researchers must have thought it represented a eurypterid at first, as its fossils were included in a plate otherwise only featuring fossils of Pterygotus , they dismissed the idea in the explanatory text of the specimens by saying that the specimen had been "accidentally introduced into this plate". Instead, the two researchers considered the fossil to likely represent the remains of some sort of crustacean.^[1]^[3]

In 1870, the specimen was fully described with the new genus name Necrogammarus by Henry Woodward. The generic name means "dead lobster", deriving from Ancient Greek νεκρός (nekrós, “dead body”)^[4] and Latin gammarus ("lobster"),^[5] and the species was designated as N. salweyi, the name honoring Humphrey Salwey, who had originally discovered the fossil. Woodward agreed with Huxley's and Salter's view of the specimen as a crustacean, referring it to the order Amphipoda.^[1]^[6]

Based on the fact that the fossil appeared to preserve diplosegments (fused pairs of arthropod segments) and a uniramous limb (a limb composed of a single series of segments attached end-to-end), the geologist Ben Peach concluded that the fossil could not be of a crustacean (as their limbs are often not uniramous) and instead referred it to the class Diplopoda in 1899, classifying it as a millipede.^[1]^[7] Peach had however never examined the holotype in person (basing his diagnosis on images alone)^[1] and some researchers, such as Henry Woods in 1909, noted that its classification was still uncertain.^[8]

In 1985, John E. Almond re-examined the Necrogammarus fossil, noting that it was a fragment of a large arthropod trunk that preserved three articulated segments, the middle one being the segment that Peach had interpreted as a diplosegment. One of the segments possess a structure identified by Peach as a uniramous limb, an identification agreed upon by Almond. As the outer segments do not appear to be double nor possess any overlap of segments in addition to the complete lack of evidence of any terrestrial habits, Almond considered the genus to tentatively represent an early aquatic relative of the Uniramia subphylum of arthropods (the group that includes myriapods, hexapods and velvet worms).^[9]

Following further examination of the fossil in 1986, Paul Selden could determine that Necrogammarus actually represented the fossil remains of a pterygotid eurypterid, the specimen representing the infracapitulum (a discrete plate formed by the fusion of the palpal coxae and the labrum) and its attached palp (the second pair of appendages).^[1]

Description and classification

The fragmentary Necrogammarus could possibly represent a fossil of either Pterygotus (top) or Erettopterus (bottom).

The specimen which morphology compared to Necrogammarus is later identified as Slimonia. Slimonia.jpg — The specimen which morphology compared to *Necrogammarus* is later identified as *Slimonia*.

Very little can confidently be stated about Necrogammarus due to its highly fragmentary nature. Selden had immediately recognized the fossil as belonging to a pterygotid eurypterid due to recently having studied the feeding mechanism of the pterygotid Erettopterusbilobus. Erettopterus possessed only three pairs of slender walking legs (typically, eurypterids with swimming legs possess four), the first pair of walking legs being reduced to a small palp. The coxae and labrum of this palp are fused into a structure that is known as the infracapitulum. Comparison between Necrogammarus and specimens of Erettopterus reveals that Necrogammarus represents the infracapitulum and palp of a large pterygotid.^[1] The entire specimen excluding the palp measures about 70 millimetres (2.8 in) across from side to side, with the palp measuring about 45 millimetres (1.8 in).^[1] In 2023 however, a specimen of E. bilobus that is compared to morphology of Necrogammarus is identified as specimen of Slimonia instead.^[10]

Two other pterygotids (and numerous unidentifiable fragments referred to the group) are known from the same locality as Necrogammarus, Pterygotus arcuatus and Erettopterus marstoni.^[1] Both of these species are moderately-sized animals, P. arcuatus reaching lengths of 60 centimetres (24 in) and E. marstoni reaching lengths of 70 centimetres (28 in).^[11] As both of these species and the genera they are assigned to are diagnosed based on features of the telson (the posteriormost segment of the body), chelicerae (frontal appendages), coxae and the metastoma (a large plate that is part of the abdomen), it is impossible to assign Necrogammarus to either since the Necrogammarus specimen lacks said body parts. It is possible that it represents a fragment of either of them or a distinct genus.^[1]

There are several features that are shared between all pterygotids and thus very likely were present in Necrogammarus as well. The outer surface of their exoskeletons was covered in an ornamentation of semilunar scales unseen in other eurypterid groups and their appendages lacked spines (unlike many other groups, particularly primitive pterygotioids).^[12] The telson was expanded and flattened and possessed a small median keel. In Pterygotus the telson ended in a short spine whilst in Erettopterus, it was indented giving a bilobed appearance.^[13] The chelicerae (the first pair of appendages), typically small and used to aid in feeding in other eurypterid groups, were robust and gigantic in pterygotids, with strong developed teeth on specialized claws. These claws are thought to have been used in prey capture.^[14]

Paleoecology

Aside from Pterygotus arcuatus and Erettopterus marstoni, the Ludlow-aged sediments of the Welsh Borderland in England have also yielded other eurypterids indicative of an established eurypterid fauna, including representatives of the genera Salteropterus and Carcinosoma .^[15] Other than eurypterids, the Ludlow-aged deposits at Leintwardine have also yielded remains of several genera of extinct microplankton,^[16] as well as a diverse fauna of asterozoans (the group that includes starfish and brittle stars) compromising at least 16 distinct species. Other local fauna includes xiphosurans, phyllocarids, crinoids, echinoids and ophiocistioids.^[17] The environment appears to have mainly been sub-marine, with deposits indicating that the local fauna lived in channels connected to a larger body of water.^[17]

Related Research Articles

Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is likely to have appeared first either during the Early Ordovician or Late Cambrian period. With approximately 250 species, the Eurypterida is the most diverse Paleozoic chelicerate order. Following their appearance during the Ordovician, eurypterids became major components of marine faunas during the Silurian, from which the majority of eurypterid species have been described. The Silurian genus Eurypterus accounts for more than 90% of all known eurypterid specimens. Though the group continued to diversify during the subsequent Devonian period, the eurypterids were heavily affected by the Late Devonian extinction event. They declined in numbers and diversity until becoming extinct during the Permian–Triassic extinction event 251.9 million years ago.

Eurypterus is an extinct genus of eurypterid, a group of organisms commonly called "sea scorpions". The genus lived during the Silurian period, from around 432 to 418 million years ago. Eurypterus is by far the most well-studied and well-known eurypterid. Eurypterus fossil specimens probably represent more than 95% of all known eurypterid specimens.

Pterygotus is a genus of giant predatory eurypterid, a group of extinct aquatic arthropods. Fossils of Pterygotus have been discovered in deposits ranging in age from Middle Silurian to Late Devonian, and have been referred to several different species. Fossils have been recovered from four continents; Australia, Europe, North America and South America, which indicates that Pterygotus might have had a nearly cosmopolitan (worldwide) distribution. The type species, P. anglicus, was described by Swiss naturalist Louis Agassiz in 1839, who gave it the name Pterygotus, meaning "winged one". Agassiz mistakenly believed the remains were of a giant fish; he would only realize the mistake five years later in 1844.

Hibbertopterus is a genus of eurypterid, a group of extinct aquatic arthropods. Fossils of Hibbertopterus have been discovered in deposits ranging from the Devonian period in Belgium, Scotland and the United States to the Carboniferous period in Scotland, Ireland, the Czech Republic and South Africa. The type species, H. scouleri, was first named as a species of the significantly different Eurypterus by Samuel Hibbert in 1836. The generic name Hibbertopterus, coined more than a century later, combines his name and the Greek word πτερόν (pteron) meaning "wing".

Slimonia is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Slimonia have been discovered in deposits of Silurian age in South America and Europe. Classified as part of the family Slimonidae alongside the related Salteropterus, the genus contains three valid species, S. acuminata from Lesmahagow, Scotland, S. boliviana from Cochabamba, Bolivia and S. dubia from the Pentland Hills of Scotland and one dubious species, S. stylops, from Herefordshire, England. The generic name is derived from and honors Robert Slimon, a fossil collector and surgeon from Lesmahagow.

<i>Mixopterus</i> Extinct genus of arthropods

Mixopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Mixopterus have been discovered in deposits from Late Silurian age, and have been referred to several different species. Fossils have been recovered from two continents; Europe and North America.

Carcinosoma is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Carcinosoma are restricted to deposits of late Silurian age. Classified as part of the family Carcinosomatidae, which the genus lends its name to, Carcinosoma contains seven species from North America and Great Britain.

Hughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Hughmilleria have been discovered in deposits of the Silurian age in China and the United States. Classified as part of the basal family Hughmilleriidae, the genus contains three species, H. shawangunk from the eastern United States, H. socialis from Pittsford, New York, and H. wangi from Hunan, China. The genus is named in honor of the Scottish geologist Hugh Miller.

Acutiramus is a genus of giant predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Acutiramus have been discovered in deposits of Late Silurian to Early Devonian age. Eight species have been described, five from North America and two from the Czech Republic. The generic name derives from Latin acuto and Latin ramus ("branch"), referring to the acute angle of the final tooth of the claws relative to the rest of the claw.

<i>Jaekelopterus</i> Extinct Devonian genus of the Eurypterida (sea scorpions)

Jaekelopterus is a genus of predatory eurypterid, a group of extinct aquatic arthropods. Fossils of Jaekelopterus have been discovered in deposits of Early Devonian age, from the Pragian and Emsian stages. There are two known species: the type species J. rhenaniae from brackish to fresh water strata in the Rhineland, and J. howelli from estuarine strata in Wyoming. The generic name combines the name of German paleontologist Otto Jaekel, who described the type species, and the Greek word πτερόν (pteron) meaning "wing".

Salteropterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Salteropterus have been discovered in deposits of Late Silurian age in Britain. Classified as part of the family Slimonidae, the genus contains one known valid species, S. abbreviatus, which is known from fossils discovered in Herefordshire, England, and a dubious species, S. longilabium, with fossils discovered in Leintwardine, also in Herefordshire. The generic name honours John William Salter, who originally described S. abbreviatus as a species of Eurypterus in 1859.

Holmipterus is a problematic genus of eurypterid, an extinct group of aquatic arthropods. The type and only species of Holmipterus, H. suecicus, is known from deposits of Middle Silurian age in the Sweden. The generic name honours Gerhard Holm, a renowned Swedish palaeontologist specialising in arthropods and crustaceans, and the species name suecicus is Latin for 'Swedish'.

Erettopterus is a genus of large predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Erettopterus have been discovered in deposits ranging from Early Silurian to the Early Devonian, and have been referred to several different species. Fossils have been recovered from two continents; Europe and North America. The genus name is composed by the Ancient Greek words ἐρέττω (eréttō), which means "rower", and πτερόν (pterón), which means "wing", and therefore, "rower wing".

Pterygotidae is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Pterygotioidea. Pterygotids were the largest known arthropods to have ever lived with some members of the family, such as Jaekelopterus and Acutiramus, exceeding 2 metres (6.6 ft) in length. Their fossilized remains have been recovered in deposits ranging in age from 428 to 372 million years old.

Pterygotioidea is a superfamily of eurypterids, an extinct group of aquatic arthropods. Pterygotioids were the most derived members of the infraorder Diploperculata and the sister group of the adelophthalmoid eurypterids. The group includes the basal and small hughmilleriids, the larger and specialized slimonids and the famous pterygotids which were equipped with robust and powerful cheliceral claws.

Hughmilleriidae is a family of eurypterids, an extinct group of aquatic arthropods. The hughmilleriids were the most basal members of the superfamily Pterygotioidea, in contrast with the more derived families Pterygotidae and Slimonidae. Despite their classification as pterygotioids, the hughmilleriids possessed several characteristics shared with other eurypterid groups, such as the lanceolate telson.

Slimonidae is a family of eurypterids, an extinct group of aquatic arthropods. Slimonids were members of the superfamily Pterygotioidea and the family most closely related to the derived pterygotid eurypterids, which are famous for their cheliceral claws and great size. Many characteristics of the Slimonidae, such as their flattened and expanded telsons, support a close relationship between the two groups.

Herefordopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Herefordopterus is classified as part of the family Hughmilleriidae, a basal family in the highly derived Pterygotioidea superfamily of eurypterids. Fossils of the single and type species, H. banksii, have been discovered in deposits of Silurian age in Herefordshire and Shropshire, England. The genus is named after Herefordshire, where most of the Herefordopterus fossils have been found. The specific epithet honors Richard Banks, who found several well-preserved specimens, including the first Herefordopterus fossils.

Ciurcopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Ciurcopterus have been discovered in deposits of Late Silurian age in North America. Classified as part of the family Pterygotidae, the genus contains two species, C. sarlei from Pittsford, New York and C. ventricosus from Kokomo, Indiana. The genus is named in honor of Samuel J. Ciurca, Jr., who has contributed significantly to eurypterid research by discovering a large amount of eurypterid specimens, including the four specimens used to describe Ciurcopterus itself.

This timeline of eurypterid research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, and taxonomic revisions of eurypterids, a group of extinct aquatic arthropods closely related to modern arachnids and horseshoe crabs that lived during the Paleozoic Era.

References

1 2 3 4 5 6 7 8 9 10 "A new identity for the Silurian arthropod Necrogammarus | The Palaeontological Association". www.palass.org. Retrieved 2018-01-14.
↑ Morris, Samuel Francis (1980). Catalogue of the type and figured specimens of fossil Crustacea (excl. Ostracoda), Chelicerata, Myriapoda and Pycnogonida in the British Museum (Natural History). BM(NH). pp. 12. ISBN 978-0565008284.
↑ Huxley, Thomas Henry; Salter, John William (1859). On the anatomy and affinities of the genus Pterygotus and description of new species of Pterygotus. Memoirs of the Geological Survey of the United Kingdom, Monograph, 1.
↑ Meaning of necro- at www.dictionary.com. Retrieved 29 July 2018.
↑ Meaning of gammarus at latin-dictionary.net. Retrieved 17 July 2018.
↑ Woodward, Henry (1870). "On Necrogammarus salweyi (H. Woodward), an amphipodous crustacean from the Lower Ludlow of Leintwardine". Trans. Woolhope Nat. FLD Club: 271–272.
↑ Peach, Ben N. (1899). "On some new myriapods from the Palaeozoic rocks of Scotland". Proc R. Phys. Soc. Edinb. 14: 113–126.
↑ Woods, Henry (1909). Palæontology, Invertebrate (4th ed.). Cambridge University Press. p. 326.
↑ Almond, J. E. (1985). "The Silurian-Devonian Fossil Record of the Myriapoda". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 309 (1138): 227–237. Bibcode:1985RSPTB.309..227A. doi:10.1098/rstb.1985.0082. JSTOR 2396363.
↑ Bicknell, R. D. C.; Kenny, K.; Plotnick, R. E. (2023). "Ex vivo three-dimensional reconstruction of Acutiramus: a giant pterygotid sea scorpion". American Museum Novitates (4004): 1–20. doi:10.1206/4004.1. hdl:2246/7335.
↑ Lamsdell, James C.; Braddy, Simon J. (2009-10-14). "Cope's Rule and Romer's theory: patterns of diversity and gigantism in eurypterids and Palaeozoic vertebrates". Biology Letters. 6 (2): 265–269. doi:10.1098/rsbl.2009.0700. PMC 2865068 . PMID 19828493. Supplemental material.
↑ Størmer, Leif (1955). "Merostomata". Treatise on Invertebrate Paleontology, Part P Arthropoda 2, Chelicerata. p. 23.
↑ Plotnick, Roy E.; Baumiller, Tomasz K. (1988-01-01). "The pterygotid telson as a biological rudder". Lethaia. 21 (1): 13–27. Bibcode:1988Letha..21...13P. doi:10.1111/j.1502-3931.1988.tb01746.x. ISSN 1502-3931.
↑ Tetlie, O. Erik; Briggs, Derek E. G. (2009-09-01). "The origin of pterygotid eurypterids (Chelicerata: Eurypterida)". Palaeontology. 52 (5): 1141–1148. Bibcode:2009Palgy..52.1141T. doi:10.1111/j.1475-4983.2009.00907.x. ISSN 1475-4983.
↑ Kjellesvig-Waering, Erik N. (1961). "The Silurian Eurypterida of the Welsh Borderland". Journal of Paleontology. 35 (4): 789–835. JSTOR 1301214.
↑ Richards, Ruth E.; Mullins, Gary L. (2003). "Upper Silurian microplankton of the Leintwardine Group, Ludlow Series, in the type Ludlow area and adjacent regions". Palaeontology. 46 (3): 557–611. Bibcode:2003Palgy..46..557R. doi: 10.1111/1475-4983.00310 . ISSN 0031-0239.
1 2 Gladwell, David J. (2018-01-14). "Asterozoans from the Ludlow Series (upper Silurian) of Leintwardine, Herefordshire, UK". Papers in Palaeontology. 4 (1): 101–160. Bibcode:2018PPal....4..101G. doi:10.1002/spp2.1101. ISSN 2056-2802. S2CID 135239943.

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[:1-1] 1 2 3 4 5 6 7 8 9 10 "A new identity for the Silurian arthropod Necrogammarus | The Palaeontological Association". www.palass.org. Retrieved 2018-01-14.

[2] Morris, Samuel Francis (1980). Catalogue of the type and figured specimens of fossil Crustacea (excl. Ostracoda), Chelicerata, Myriapoda and Pycnogonida in the British Museum (Natural History). BM(NH). pp. 12. ISBN 978-0565008284.

[3] Huxley, Thomas Henry; Salter, John William (1859). On the anatomy and affinities of the genus Pterygotus and description of new species of Pterygotus. Memoirs of the Geological Survey of the United Kingdom, Monograph, 1.

[m-4] Meaning of necro- at www.dictionary.com. Retrieved 29 July 2018.

[m2-5] Meaning of gammarus at latin-dictionary.net. Retrieved 17 July 2018.

[6] Woodward, Henry (1870). "On Necrogammarus salweyi (H. Woodward), an amphipodous crustacean from the Lower Ludlow of Leintwardine". Trans. Woolhope Nat. FLD Club: 271–272.

[7] Peach, Ben N. (1899). "On some new myriapods from the Palaeozoic rocks of Scotland". Proc R. Phys. Soc. Edinb. 14: 113–126.

[8] Woods, Henry (1909). Palæontology, Invertebrate (4th ed.). Cambridge University Press. p. 326.

[9] Almond, J. E. (1985). "The Silurian-Devonian Fossil Record of the Myriapoda". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 309 (1138): 227–237. Bibcode:1985RSPTB.309..227A. doi:10.1098/rstb.1985.0082. JSTOR 2396363.

[10] Bicknell, R. D. C.; Kenny, K.; Plotnick, R. E. (2023). "Ex vivo three-dimensional reconstruction of Acutiramus: a giant pterygotid sea scorpion". American Museum Novitates (4004): 1–20. doi:10.1206/4004.1. hdl:2246/7335.

[:3-11] Lamsdell, James C.; Braddy, Simon J. (2009-10-14). "Cope's Rule and Romer's theory: patterns of diversity and gigantism in eurypterids and Palaeozoic vertebrates". Biology Letters. 6 (2): 265–269. doi:10.1098/rsbl.2009.0700. PMC 2865068 . PMID 19828493. Supplemental material.

[:4-12] Størmer, Leif (1955). "Merostomata". Treatise on Invertebrate Paleontology, Part P Arthropoda 2, Chelicerata. p. 23.

[:12-13] Plotnick, Roy E.; Baumiller, Tomasz K. (1988-01-01). "The pterygotid telson as a biological rudder". Lethaia. 21 (1): 13–27. Bibcode:1988Letha..21...13P. doi:10.1111/j.1502-3931.1988.tb01746.x. ISSN 1502-3931.

[:0-14] Tetlie, O. Erik; Briggs, Derek E. G. (2009-09-01). "The origin of pterygotid eurypterids (Chelicerata: Eurypterida)". Palaeontology. 52 (5): 1141–1148. Bibcode:2009Palgy..52.1141T. doi:10.1111/j.1475-4983.2009.00907.x. ISSN 1475-4983.

[:32-15] Kjellesvig-Waering, Erik N. (1961). "The Silurian Eurypterida of the Welsh Borderland". Journal of Paleontology. 35 (4): 789–835. JSTOR 1301214.

[16] Richards, Ruth E.; Mullins, Gary L. (2003). "Upper Silurian microplankton of the Leintwardine Group, Ludlow Series, in the type Ludlow area and adjacent regions". Palaeontology. 46 (3): 557–611. Bibcode:2003Palgy..46..557R. doi: 10.1111/1475-4983.00310 . ISSN 0031-0239.

[:2-17] 1 2 Gladwell, David J. (2018-01-14). "Asterozoans from the Ludlow Series (upper Silurian) of Leintwardine, Herefordshire, UK". Papers in Palaeontology. 4 (1): 101–160. Bibcode:2018PPal....4..101G. doi:10.1002/spp2.1101. ISSN 2056-2802. S2CID 135239943.

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